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 * Copyright (c) 2005, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package com.sun.source.util;

import com.sun.source.tree.*;

/**
 * A TreeVisitor that visits all the child tree nodes.
 * To visit nodes of a particular type, just override the
 * corresponding visitXYZ method.
 * Inside your method, call super.visitXYZ to visit descendant
 * nodes.
 *
 * <p>The default implementation of the visitXYZ methods will determine
 * a result as follows:
 * <ul>
 * <li>If the node being visited has no children, the result will be null.
 * <li>If the node being visited has one child, the result will be the
 * result of calling {@code scan} on that child. The child may be a simple node
 * or itself a list of nodes.
 * <li> If the node being visited has more than one child, the result will
 * be determined by calling {@code scan} each child in turn, and then combining the
 * result of each scan after the first with the cumulative result
 * so far, as determined by the {@link #reduce} method. Each child may be either
 * a simple node of a list of nodes. The default behavior of the {@code reduce}
 * method is such that the result of the visitXYZ method will be the result of
 * the last child scanned.
 * </ul>
 *
 * <p>Here is an example to count the number of identifier nodes in a tree:
 * <pre>
 *   class CountIdentifiers extends TreeScanner&lt;Integer,Void&gt; {
 *      {@literal @}Override
 *      public Integer visitIdentifier(IdentifierTree node, Void p) {
 *          return 1;
 *      }
 *      {@literal @}Override
 *      public Integer reduce(Integer r1, Integer r2) {
 *          return (r1 == null ? 0 : r1) + (r2 == null ? 0 : r2);
 *      }
 *   }
 * </pre>
 *
 * @author Peter von der Ah&eacute;
 * @author Jonathan Gibbons
 * @since 1.6
 */
@jdk.Exported
public class TreeScanner<R, P> implements TreeVisitor<R, P> {

  /**
   * Scan a single node.
   */
  public R scan(Tree node, P p) {
    return (node == null) ? null : node.accept(this, p);
  }

  private R scanAndReduce(Tree node, P p, R r) {
    return reduce(scan(node, p), r);
  }

  /**
   * Scan a list of nodes.
   */
  public R scan(Iterable<? extends Tree> nodes, P p) {
    R r = null;
    if (nodes != null) {
      boolean first = true;
      for (Tree node : nodes) {
        r = (first ? scan(node, p) : scanAndReduce(node, p, r));
        first = false;
      }
    }
    return r;
  }

  private R scanAndReduce(Iterable<? extends Tree> nodes, P p, R r) {
    return reduce(scan(nodes, p), r);
  }

  /**
   * Reduces two results into a combined result.
   * The default implementation is to return the first parameter.
   * The general contract of the method is that it may take any action whatsoever.
   */
  public R reduce(R r1, R r2) {
    return r1;
  }


/* ***************************************************************************
 * Visitor methods
 ****************************************************************************/

  public R visitCompilationUnit(CompilationUnitTree node, P p) {
    R r = scan(node.getPackageAnnotations(), p);
    r = scanAndReduce(node.getPackageName(), p, r);
    r = scanAndReduce(node.getImports(), p, r);
    r = scanAndReduce(node.getTypeDecls(), p, r);
    return r;
  }

  public R visitImport(ImportTree node, P p) {
    return scan(node.getQualifiedIdentifier(), p);
  }

  public R visitClass(ClassTree node, P p) {
    R r = scan(node.getModifiers(), p);
    r = scanAndReduce(node.getTypeParameters(), p, r);
    r = scanAndReduce(node.getExtendsClause(), p, r);
    r = scanAndReduce(node.getImplementsClause(), p, r);
    r = scanAndReduce(node.getMembers(), p, r);
    return r;
  }

  public R visitMethod(MethodTree node, P p) {
    R r = scan(node.getModifiers(), p);
    r = scanAndReduce(node.getReturnType(), p, r);
    r = scanAndReduce(node.getTypeParameters(), p, r);
    r = scanAndReduce(node.getParameters(), p, r);
    r = scanAndReduce(node.getReceiverParameter(), p, r);
    r = scanAndReduce(node.getThrows(), p, r);
    r = scanAndReduce(node.getBody(), p, r);
    r = scanAndReduce(node.getDefaultValue(), p, r);
    return r;
  }

  public R visitVariable(VariableTree node, P p) {
    R r = scan(node.getModifiers(), p);
    r = scanAndReduce(node.getType(), p, r);
    r = scanAndReduce(node.getNameExpression(), p, r);
    r = scanAndReduce(node.getInitializer(), p, r);
    return r;
  }

  public R visitEmptyStatement(EmptyStatementTree node, P p) {
    return null;
  }

  public R visitBlock(BlockTree node, P p) {
    return scan(node.getStatements(), p);
  }

  public R visitDoWhileLoop(DoWhileLoopTree node, P p) {
    R r = scan(node.getStatement(), p);
    r = scanAndReduce(node.getCondition(), p, r);
    return r;
  }

  public R visitWhileLoop(WhileLoopTree node, P p) {
    R r = scan(node.getCondition(), p);
    r = scanAndReduce(node.getStatement(), p, r);
    return r;
  }

  public R visitForLoop(ForLoopTree node, P p) {
    R r = scan(node.getInitializer(), p);
    r = scanAndReduce(node.getCondition(), p, r);
    r = scanAndReduce(node.getUpdate(), p, r);
    r = scanAndReduce(node.getStatement(), p, r);
    return r;
  }

  public R visitEnhancedForLoop(EnhancedForLoopTree node, P p) {
    R r = scan(node.getVariable(), p);
    r = scanAndReduce(node.getExpression(), p, r);
    r = scanAndReduce(node.getStatement(), p, r);
    return r;
  }

  public R visitLabeledStatement(LabeledStatementTree node, P p) {
    return scan(node.getStatement(), p);
  }

  public R visitSwitch(SwitchTree node, P p) {
    R r = scan(node.getExpression(), p);
    r = scanAndReduce(node.getCases(), p, r);
    return r;
  }

  public R visitCase(CaseTree node, P p) {
    R r = scan(node.getExpression(), p);
    r = scanAndReduce(node.getStatements(), p, r);
    return r;
  }

  public R visitSynchronized(SynchronizedTree node, P p) {
    R r = scan(node.getExpression(), p);
    r = scanAndReduce(node.getBlock(), p, r);
    return r;
  }

  public R visitTry(TryTree node, P p) {
    R r = scan(node.getResources(), p);
    r = scanAndReduce(node.getBlock(), p, r);
    r = scanAndReduce(node.getCatches(), p, r);
    r = scanAndReduce(node.getFinallyBlock(), p, r);
    return r;
  }

  public R visitCatch(CatchTree node, P p) {
    R r = scan(node.getParameter(), p);
    r = scanAndReduce(node.getBlock(), p, r);
    return r;
  }

  public R visitConditionalExpression(ConditionalExpressionTree node, P p) {
    R r = scan(node.getCondition(), p);
    r = scanAndReduce(node.getTrueExpression(), p, r);
    r = scanAndReduce(node.getFalseExpression(), p, r);
    return r;
  }

  public R visitIf(IfTree node, P p) {
    R r = scan(node.getCondition(), p);
    r = scanAndReduce(node.getThenStatement(), p, r);
    r = scanAndReduce(node.getElseStatement(), p, r);
    return r;
  }

  public R visitExpressionStatement(ExpressionStatementTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitBreak(BreakTree node, P p) {
    return null;
  }

  public R visitContinue(ContinueTree node, P p) {
    return null;
  }

  public R visitReturn(ReturnTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitThrow(ThrowTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitAssert(AssertTree node, P p) {
    R r = scan(node.getCondition(), p);
    r = scanAndReduce(node.getDetail(), p, r);
    return r;
  }

  public R visitMethodInvocation(MethodInvocationTree node, P p) {
    R r = scan(node.getTypeArguments(), p);
    r = scanAndReduce(node.getMethodSelect(), p, r);
    r = scanAndReduce(node.getArguments(), p, r);
    return r;
  }

  public R visitNewClass(NewClassTree node, P p) {
    R r = scan(node.getEnclosingExpression(), p);
    r = scanAndReduce(node.getIdentifier(), p, r);
    r = scanAndReduce(node.getTypeArguments(), p, r);
    r = scanAndReduce(node.getArguments(), p, r);
    r = scanAndReduce(node.getClassBody(), p, r);
    return r;
  }

  public R visitNewArray(NewArrayTree node, P p) {
    R r = scan(node.getType(), p);
    r = scanAndReduce(node.getDimensions(), p, r);
    r = scanAndReduce(node.getInitializers(), p, r);
    r = scanAndReduce(node.getAnnotations(), p, r);
    for (Iterable<? extends Tree> dimAnno : node.getDimAnnotations()) {
      r = scanAndReduce(dimAnno, p, r);
    }
    return r;
  }

  public R visitLambdaExpression(LambdaExpressionTree node, P p) {
    R r = scan(node.getParameters(), p);
    r = scanAndReduce(node.getBody(), p, r);
    return r;
  }

  public R visitParenthesized(ParenthesizedTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitAssignment(AssignmentTree node, P p) {
    R r = scan(node.getVariable(), p);
    r = scanAndReduce(node.getExpression(), p, r);
    return r;
  }

  public R visitCompoundAssignment(CompoundAssignmentTree node, P p) {
    R r = scan(node.getVariable(), p);
    r = scanAndReduce(node.getExpression(), p, r);
    return r;
  }

  public R visitUnary(UnaryTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitBinary(BinaryTree node, P p) {
    R r = scan(node.getLeftOperand(), p);
    r = scanAndReduce(node.getRightOperand(), p, r);
    return r;
  }

  public R visitTypeCast(TypeCastTree node, P p) {
    R r = scan(node.getType(), p);
    r = scanAndReduce(node.getExpression(), p, r);
    return r;
  }

  public R visitInstanceOf(InstanceOfTree node, P p) {
    R r = scan(node.getExpression(), p);
    r = scanAndReduce(node.getType(), p, r);
    return r;
  }

  public R visitArrayAccess(ArrayAccessTree node, P p) {
    R r = scan(node.getExpression(), p);
    r = scanAndReduce(node.getIndex(), p, r);
    return r;
  }

  public R visitMemberSelect(MemberSelectTree node, P p) {
    return scan(node.getExpression(), p);
  }

  public R visitMemberReference(MemberReferenceTree node, P p) {
    R r = scan(node.getQualifierExpression(), p);
    r = scanAndReduce(node.getTypeArguments(), p, r);
    return r;
  }

  public R visitIdentifier(IdentifierTree node, P p) {
    return null;
  }

  public R visitLiteral(LiteralTree node, P p) {
    return null;
  }

  public R visitPrimitiveType(PrimitiveTypeTree node, P p) {
    return null;
  }

  public R visitArrayType(ArrayTypeTree node, P p) {
    return scan(node.getType(), p);
  }

  public R visitParameterizedType(ParameterizedTypeTree node, P p) {
    R r = scan(node.getType(), p);
    r = scanAndReduce(node.getTypeArguments(), p, r);
    return r;
  }

  public R visitUnionType(UnionTypeTree node, P p) {
    return scan(node.getTypeAlternatives(), p);
  }

  public R visitIntersectionType(IntersectionTypeTree node, P p) {
    return scan(node.getBounds(), p);
  }

  public R visitTypeParameter(TypeParameterTree node, P p) {
    R r = scan(node.getAnnotations(), p);
    r = scanAndReduce(node.getBounds(), p, r);
    return r;
  }

  public R visitWildcard(WildcardTree node, P p) {
    return scan(node.getBound(), p);
  }

  public R visitModifiers(ModifiersTree node, P p) {
    return scan(node.getAnnotations(), p);
  }

  public R visitAnnotation(AnnotationTree node, P p) {
    R r = scan(node.getAnnotationType(), p);
    r = scanAndReduce(node.getArguments(), p, r);
    return r;
  }

  public R visitAnnotatedType(AnnotatedTypeTree node, P p) {
    R r = scan(node.getAnnotations(), p);
    r = scanAndReduce(node.getUnderlyingType(), p, r);
    return r;
  }

  public R visitOther(Tree node, P p) {
    return null;
  }

  public R visitErroneous(ErroneousTree node, P p) {
    return null;
  }
}
